Plasma, which is generated inside a vacuum chamber, is being widely used in unit processes such as dry etching, physical or chemical vapor deposition, sensitizer cleaning, or other surface treatments. In order to generate plasma, there are installed antennas on the upper inside or outside of the plasma chamber and a target holder on the lower portion of the chamber. By supplying the high frequency electric power into upper inside space of the chamber through the antennas, a processing gas inside the chamber is dissociated and the plasma is generated by glow discharge. When the bias voltage applies to the target holder, the generated plasma hits and treats the surface of the target such as wafer.
As semiconductor chips are highly integrated and semiconductor wafers or liquid crystal displays are becoming the larger area, the required conditions on the apparatus for processing the surface of a target are getting stricter and plasma processing apparatus is under the same situation. Many studies and suggestions have been made to improve the efficiency of the plasma processing apparatus. Such studies and suggestions are focused on increasing the density of: plasma in order to reduce the time required for treating a target, and on generating uniformly distributed plasma to treat a target with a larger area. Especially, in terms of increasing the plasma density, the inductively coupled plasma source is widely used. Changing the shape or location of antenna and changing the location through which a processing gas is supplied are attempted to generate the uniform plasma.
In spite of such efforts, plasma processing methods naturally suffered from that plasma is a charged particle, as thus, super-finely treated target can not be obtained. For instance, use of the charged particles for etching often tends to charge the target being etched, which may alter the etch profile, or lead to voltage gradients which may damage the performance of the device formed on the target. Further, the etching reaction by accelerated ions may result in the formation of damaged layers as a result of the dislocation on the surface of a substrate or the formation of deformed surface layers. Therefore, additional treatments such as heat treatment are required to heal such damage.
To overcome such a problem with the plasma processing method, a system using neutral particles instead of plasma is suggested in U.S. Pat. No. 4,662,977 (Title of the invention: neutral particle surface alteration) issued on May 5, 1987. This system produces neutral particles beams by creating plasma with plasma gun and directing the plasma towards an inclined metal plate. Nevertheless, this system is not suitable for treating the surface of a target having 8 inches or more, because of the small cross section of the incident neutral particle beams onto wafers. For the application to the larger target, it is difficult for this system to guarantee the uniformity of the etch profile. Moreover, this system is designed to directly convert atoms or molecules of the active species for etching to plasma, and flux of hyperthermal neutral particle beams from this system is much less than the one from the conventional plasma processing apparatus. Thus, the processing time is very long, thus, not economical.